1. Field of the Invention
This invention relates to an unsaturated polyester having a large molecular weight and which is useful in the fields of fiber reinforced plastics, linings and castings and a high molecular unsaturated polyester made by blending with this unsaturated polyester a monomer that is copolymerizable therewith.
2. Discussion of the Background
As is well known, unsaturated polyester resins (polyester resins), known as typical radical curing type resins, are widely used as fiber reinforced plastics (hereinafter referred to as FRP), coating materials, lining materials, casting materials and the like.
With the expanded use of unsaturated polyester resins, physical properties required of the resins have, of course, become of a high degree and various methods for improving the properties of this kind of resin have therefore been practiced. For example, methods of improving mechanical properties based on increasing the molecular weight by reaction with diisocyanate, of improving coating performance by reaction with an epoxy resin, and of providing a toughness by using a rubber-like polymer are being practical.
However there is no movement visible at the publicly disclosed level towards solving the problems by increasing the molecular weight of an unsaturated polyester (unsaturated alkyd) constituting an unsaturated polyester resin.
This may be because it is thought that the molecular weight (hereinafter expressed as number-average molecular weight) is at most 2,000 to 2,500 and that it would be very difficult to exceed 3,000 because of gelation during reaction.
ln fact, for desired practicality of resulting resins in terms of handling relating to viscosity, curing, moldability and other factors, it is difficult to crack the barrier of a molecular weight of 3,000 only by the esterification reaction ordinarily used for manufacture of unsaturated polyester resins.
An object of the present invention is to provide a novel high molecular unsaturated polyester having improved physical properties and which is widely applicable.